Effects of Selective Logging on Low Flows and Water Yield in a Coastal Stream in Northern California

摘要

Using a low flow season defined as a function of antecedent precipitation, streamflow data for a 21 year period was analyzed to determine the effects of selective tractor harvesting of second-growth Douglas-fir and redwood forest on the volume, timing, and duration of low flows. and annual water yield. Significant increases in streamflow were detected for both the annual period and the low flow season. Maximum increases were realized the year following the completion. of logging. Greater relative increases were witnessed for the summer low flow period, however these increases were short-lived in comparison to the overall increase in annual water yield. Logging factors were found to be the most influential variables in describing flow differences between the control and treated watersheds. Summer flow increases were well correlated with the percent of the watershed area logged when this variable was defined to represent revegetation effects as a function of time since logging. In contrast, the enhancement of annual yield (predominately winter flows) was well correlated to the percent of the watershed area converted to roads, landings, and skid trails (15%). The flow response to logging was found to be highly variable. Some of this variablility was correlated to antecedent precipitation conditions, although much was unexplained. It was concluded that the potential augmentation of water yields resulting from harvest in north coastal California watersheds would be of minimal value as a management option for meeting specific water demand levels.